The road to recovery is long and filled with potholes
If we’re going to change the conversation from species extinction to species recovery we have to take new directions.
Australia – not quite the gold standard
At least 23 mammal species have become extinct since European settlement, in large part to introduced predators, especially the red fox, alongside habitat destruction. A previous blog has mentioned the story of the Christmas Island pipistrelle. Species extinction has been prevented in many species through constructing predator-proof fences. Currently there are several species which exist only in highly managed relict populations, the eastern barred bandicoot is one of these species.
Where there’s a fence there’s a way
Once thought extinct, a few eastern barred bandicoots were found hiding in a tip and evacuated to Melbourne Zoo. After successfully breeding in captivity, reintroduction was attempted at several sites. However, success only occurred at larger sites with constant site management and fence maintenance. Without predators herbivore populations, rabbits and macropods, increased significantly causing habitat degradation, which in conjunction with drought, fire and possible fence breaches caused the extinction of several sites.
In July last year reintroduction occurred at Woodlands Historic Park, which is just east of Melbourne Airport. The population can be followed here.
Beyond the fence
Placing a species behind a fence does not mean it is safe. Because of this the eastern barred bandicoot remains ‘extinct in the wild’. Fences remain vulnerable to tree falls, native animals such as large male kangaroos and digging echidnas and, unfortunately, vandalism all of which can give the ever-wily fox a chance to slip in. Although control follows swiftly after, foxes are extremely cunning and whenever a fox has entered, a population decline has followed.
Beyond the threat of predation, small populations of any species remain vulnerable to drought, disease, fire and crucially inbreeding. Many threatened species require human assisted translocation of individuals between populations to maintain gene-flow. This can include maintaining expensive captive breeding populations too.
An approach that is set to increase with climate change is assisted colonisation, which can serve a variety of purposes. Largely it has been discussed in relation to restoring ecosystem function should an important species become extinct. In such a circumstance a species would be introduced to an ecosystem that occupies a similar niche and performs a similar function to the extinct species.
Alternatively, assisted colonisation can be used for the conservation of species. It is a last resort when human impacts have become overwhelming in a species native distribution. Unfortunately this is the case in Australia and New Zealand where introduced predators have wreaked havoc on native populations. Species such as takahe, tuatara and several small Australian marsupial species have been introduced to offshore and mainland (fenced) islands to offer security until threats are abated in their native range. For the mala, or rufous hare-wallaby, this action has allowed its status to be upgraded from extinct in the wild to endangered.
The devil in the room
Unfortunately the threat doesn’t end with foxes. Conservation scientists have growing concerns about the increasing threats posed by feral cats. Recent articles from Radio National and ABC news explore the issue. Not only have cats benefited from the control of foxes, it seems the demise of the Tasmanian devil has also been a boon for cats. As the devil facial tumour disease has led to rapid declines in devil populations, feral cat populations have subsequently increased. To complicate the issue feral cats pose a threat on two fronts, predation and disease.
Cats are the host of a parasite which causes toxoplasmosis. As they did not evolve alongside cats, Australian marsupials are particularly vulnerable to the disease. Unfortunately, little is known about the effect the disease could have on populations but it is likely that threatened species will be more vulnerable due to their restricted genetic diversity. Complicating the issue is the difficulty of cat control and the unknown link between cat demographics and incidence of toxoplasmosis.
Currently cat eradication is only feasible on small, unpopulated islands so alternative strategies must be sought. One possibility is reintroducing a competitor such as the Tasmanian devil. The devil was likely extirpated from the mainland with the arrival of dingoes 3000 years ago. Such a reintroduction would have the added benefit of aiding devil conservation with growing concerns about the loss of natural behaviours the longer devils remain in captivity. Managers are planning to trial reintroducing the devil to Wilson’s Promontory. See here and here for more.
In a continually changing environment, alternative approaches such as these are increasingly important.